Method of and arrangement for the seasonal storage and use of hot water produced in particular by electrical power-generating thermal and nuclear stations

ABSTRACT

A large capacity tank for the seasonal storage of hot water from electrical power-generating thermal and nuclear plants to be used seasonally to heat buildings, consisting of a large basin which comprises partitions dividing the basin into several portions communicating with each other in parallel and/or series relationship, at least one hot water supply input from said plants, leading to the distribution systems which open into one portion of the basin and at least one cold make-up and/or return water supply input for the distribution systems opening into another portion of said basin.

This is a division, of application Ser. No. 668,000, filed Mar. 18,1976, now U.S. Pat. No. 4,159,736.

BACKGROUND OF THE INVENTION

The present invention relates to a method and to plants or arrangementsenabling for seasonal storage and use of hot water produced inparticular by electrical power-generating thermal and nuclear plants orstations.

The Applicant has already disclosed previously in U.S. patentapplication Ser. No. 574,418, filed on May 5, 1975 under entitled"Method and plants for producing, Storing, Modulating and DistributingEnergy", now U.S. Pat. No. 3,996,749, means adapted to use in particularfor district heating purposes and for various industrial applicationsthe huge amounts of heat presently wastefully lost or discharged to thedetriment of the ecology from electrical power-generating thermal andnuclear stations. The invention forming the subject matter of theabove-mentioned U.S. patent actually enables to multiply with a factorusually ranging from 1 to 5 and according to the operating requirementsand lay-out conditions the available power supplied by the existingpower plants consuming given amounts of fuel.

The present invention brings about new improvements to such kinds ofarrangements by enabling in a particularly convenient, effective,economical and profitable manner the seasonal storage of the excess heatpower generated by in particular thermal and nuclear plants during thewarm season (extending in particular from the beginning of April to theend of August) and the use of these heat excesses more particularlyduring the cold season (in particular between October and the end ofJanuary).

SUMMARY OF THE INVENTION

An arrangement according to the invention enabling such a seasonalstorage comprises in particular a large capacity tank which ischaracterized in that it comprises a basin having a large area, providedsubstantially on ground level and comprising partition walls dividingthe basin into several portions which communicate with one another inparallel and/or in series connected relationship, at least one hot watersupply input from said power stations leading to the utilization ofdistributing systems opening into one portion of the basin and at leastone cold make-up and/or return supply input from the utilization ordistributing systems opening into another portion of said basin. Theseparating portions advantageously exhibit very great lengths withrespect to their widths and to their depths and communicate with eachother in parallel and/or in series connected relationship with theiradjacent longitudinal ends. It is thus possible, provided that there area minimum number of systems or pipelines and a minimum number of pumps,to provide in an effective and economical manner on surfaces ofrelatively reduced areas seasonal storages of huge amounts of heat whichmay afterwards be recovered during the desired time periods inparticular for purposes of heating buildings as well as for meetingother industrial needs.

According to another novel characterizing feature of the presentinvention said basins for the storage of hot water are filled with amechanically strong porous structure such as gravel and pebbles or thelike. When covering the top surface of said porous structure of saidbasins with an impervious, that is leakage-proof or fluid-tight layermade for instance from concrete or asphalt, it is possible tosubsequently cover said surface with tillable soil or tilth which willenable to grow or farm various plants under glass or in greenhouses inany season, the glasshouses or greenhouses being heated by the losses orwastes, adjusted to a desirable extent, of a part of the heat storedwithin the basins. Such an approach seems to be very advantageous in thecase where the porous structure of pebbles or gravel is alreadyavailable on the spot, in particular along some river valleys.

When such a porous structure is not available beforehand, otherapproaches may be contemplated advantageously.

Thus for instance the tank may be designed so that the storage areas orportions to which are leading the hot water supply systems of the powerstations and those to which are leading the cold make-up and/or returnwater supply inputs from the utilization systems are in contact with oneanother while being separated by at least one movable, yielding ordeformable membrane or like diaphragm which separates said storage areasinto at least one hot water storage body or space and at least one coldwater storage body or space which added together form a substantiallyconstant volume of storage water. When proceeding that way it ispossible to provide within a basin economical structures enabling thestorage of hot water and cold water the substantially invariable volumesof which will avoid any problems which could be raised or encounteredwith large capacity seasonal storages of water and variations in thefilling levels of the basins.

In such a case and according to a preferred form of the invention, theupper storage portions have an insulating roof above which is provided awater surface or lake or pool the bottom of which is said roof. Thus iseconomically provided an artificial lake the water surface of which maybe tempered at will and used for instance for fish-farming orfish-breeding purposes, for aquatic sports purposes and so on.

According to the invention, there is moreover provided a method of usingor working and operating a tank of the aforesaid kind wherein water witha specific gravity or density and/or saltness lower than those of saidstorage hot and cold water is used for filling up the holding space ofsaid lake or water surface. Thereby is automatically achieved thebuilding up of overlying strata or layers in the upward direction whichis normally the following from bottom to top: cold water storage ofhigher density or specific gravity, hot water storage of intermediatedensity or specific gravity, cold lake water of lower density orspecific gravity. The hot storage water is thus entrapped between tworelatively cold or warm water layers which will prevent heat losses tothe atmosphere and to the ground owing to the low conductivity from onewater layer to another one when such layers may not become mixedtogether due to the provision of a separating membrane or diaphragm.Said membrane may advantageously, comprise a yielding, deformable,perfectly imputrescible film or layer of plastic material such forinstance as polyethylene or others of low cost.

Above the storage body of hot water, whether salt or not, there isalways arranged a "roof" which provides for some heat insulation of thestored hot water with respect to the upper outside such roofs. Variousforms of embodiment will be described. With the word "roof" is meant anycovering or disposed above the hot water storage body, it beingunderstood that other elements according to the embodiments used may beprovided above this covering.

According to an embodiment of the invention the structure of theinsulating "roof" is designed so as to enable not only to compensate forthe heat losses of the tank towards the outside environment but also inaddition to supply the hot water storage with additional thermal energywhich is taken from the outer light radiation-that is, from solar energylocally available.

Thus, according to an embodiment the upper part of the tank comprises aroof underneath which is stored the hot water, which roof will promotethe inward flow of outside heat due to solar radiation towards the hotwater storage and reduce the outward directed flow of heat from thestorage towards the outside.

The roof advantageously comprises for this purpose at least one lightradiation absorbing layer contacting the hot water storage and at leastone top layer allowing the major part of the light flux to traveltherethrough and reflecting the major part of the infra-red radiationre-emitted by said absorbing layer. Thus is achieved a hay box-typeabsorption and confinment effect which generally enables to compensatefor the heat losses from the storage towards the outer environmentalmedium and even usually to supply additional heat energy, thereby addingto the seasonal storage of heat from the hot waters produced by thepower stations a seasonal storage of heat generated by the radition fromthe sun.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characterizing features, objects and advantages of the inventionwill appear more clearly as the following detailed explanatorydescription proceeds with reference to the accompanying diagrammaticdrawings given by way of examples only and wherein:

FIG. 1 is a graphical chart showing the seasonal correlation between theproduction of heat rejected by the thermal and nuclear power stations inFrance and the seasonal needs in heat in particular for district heatingpurposes;

FIG. 2 is a diagrammatic view of the layout of a plant designedaccording to the invention and enabling the seasonal storage and use ofthe excess heat produced by a power-generating station;

FIG. 3 is a view in cross-section taken substantially upon the planeIII--III in FIG. 2 through the tank structure shown in FIG. 2 anddesigned according to the invention;

FIG. 4 is a longitudinal sectional view drawn on a larger scale througha tank structure of the kind illustrated in FIGS. 2 and 3;

FIG. 5 is a cross-sectional view diagrammatically showing a structure ofgrounds commonly encountered along a river;

FIG. 6 shows the structure of grounds as illustrated in FIG. 5 which hasbeen used to provide a storage tank according to the invention;

FIG. 7 diagrammatically shows a top view of the tank made as shown inFIG. 6;

FIG. 8 is a view in longitudinal section taken substantially upon theplane VIII--VIII of FIG. 7;

FIG. 9 is a view drawn on a larger scale of the encircled detail IX ofFIG. 8, showing the composition of the ground above the tank;

FIG. 10 is a diagrammatic view in cross-section through a tank accordingto an alternative embodiment;

FIG. 11 shows on a larger scale a detail construction of the connectionsat one for instance longitudinal end of the tank basin and of the heatdistributing system leading from the tank;

FIGS. 12 and 13 are diagrammatic cross-sectional views showing tanksdesigned according to two other alternative embodiments, respectively;

FIG. 14 illustrates on a larger scale a detail of the connection of thehot water and cold water storage tanks with the outside as well as adetail of the fastening means for the insulating roof of the storagemeans;

FIG. 15 is a cross-sectional view of a storage tank designed accordingto another embodiment of the invention;

FIG. 16 shows on a larger scale the encircled detail part XVI in FIG.15;

FIG. 17 is a cross-sectional view illustrating another modification;

FIG. 18 is a diagrammatic cross-sectional view showing a tank of thekind described in said U.S. Pat. No. 3,996,749; and

FIGS. 19 to 22 are sectional views of the encircled part A in FIG. 18,drawn on a larger scale and diagrammatically showing various tank roofconstructions for practicing the improvements forming the subject matterof the invention.

DETAILED DESCRIPTION

FIG. 1 which illustrates the economically interesting character of theinvention will be referred to first. In this Figure the curve C₁ givesthe amount of heat weighted over several years, discharged as waste inFrance by the thermal and nuclear power stations into the rivers or intothe atmosphere (while taking into account the overall efficiency ofelectricity production which is of about 30% to 35%), this amount ofheat being plotted as the ordinate as a function of the time period ofthe year plotted in months as the abscissa.

Likewise in this Figure the curve C₂ gives the seasonal needs in heatmore particularly for district heating purposes.

From a comparison of both curves it appears that the production of wasteheat by the power stations is higher than the heat required for the warmseason (in particular from April to August) and that it is lower thanthe heat required for the cold season (in particular from November toFebruary).

Therefore when using the "total energy" process advocated in theaforesaid U.S. patent application according to which the heat generatedby the power stations and not converted into electrical power is usedfor heating dwelling premises and for various other industrialapplications (chemical industry, soap works or like factories,wash-houses, laundry-rooms and so on) it has been found that during warmtime periods the power stations supply an excess of energy which may notbe used at that time whereas during the cold season they do not generateenough power.

When comparing both curves C₁, C₂ it appears that the hatched orshadowed area A1 between the curves C₁ and C₂ which corresponds to theamount of excess energy supplied by the power stations during the warmseasons has a surface area substantially equivalent to the added hatchedor shadowed surface areas designated at A2, A3 which show the additionalenergy requirements in the form of heat during the cold seasons whichmay not be met by the power stations. It is moreover seen that thesurface area A1=A2+A3 is about 10% of the surface area defined betweenthe curve C₁ and the axis of abscissa, i.e. corresponds to 10% of thetotal energy released as heat by the power stations.

Thus by storing a part of the excess power released by the powerstations during the warm seasons it is possible to decrease by more than20% the maximum power output of said power stations which wouldotherwise have been required to meet the demand (by absorbing the powerrequirements corresponding to the areas A2, A3 and by decreasing therequirements from 100 points to less than 80 points).

The invention advocates a specific tank and plant construction whichenables such seasonal storage of large amounts of heat and a practicallater re-use or recovery thereof while providing for a valorization ofthe sites.

The form of embodiment shown in FIGS. 2 to 4 will now be referred to.

Referring at first to FIG. 2 the reference numeral 10 designates a forinstance thermal power station which serves the purpose of generatingelectricity and which rejects hot water at a temperature of for instance70° C. to 90° C. as a waste by-product. The hot water rejected by thepower station is discharged by a pipe-line 11. The pipe-line 11 isfeeding a pipe-line 12 leading to a utilization system 13diagrammatically shown at 14, 15, 16 and 17. At the outlets of theutilization appliances 14-17 the cooled water may be drained off in partat 18 for instance towards rivers and recycled at 19 towards thepipe-line 20 feeding cold water into the power station 10. At 21 isshown a source of cold make-up water required to compensate for thelosses and wastes.

In order to enable a feedback control of the circuit there is providedat 22 a large-capacity tank for the seasonal storage of hot water inparticular during summer time and from which water may be drawn to meetthe peak requirements in particular during winter time. At 23 is shownthe connection between the pipe-line 11 for the hot water issuing fromthe power station and the tank 22 and at 24 is shown the junction of thetank 22 with the cold water circuit 19, 21. The double arrows 25, 26show that there may be an addition or input of hot water into the tank22 and a correlative drawing-off or output of cold water or reversely adrawing-off or output of hot water and a correlative addition or inputof cold water.

As clearly apparent from FIGS. 2, 3 and 4, the tank 22 is a tank with alarge surface area provided substantially on ground level 27 andcomprising partition walls 28, 29, 30, 31, 32 which divide the basininto several water retaining portions 33, 34, 35, 36 which communicatewith one another. In the example shown, the portions 33-36 communicatewith each other in series relationship through connectionsdiagrammatically shown at 37, 38, 39 at their adjacent ends 33a, 34a;34b, 35b; 35a, 36a, respectively.

According to a preferred embodiment of the invention the hollow space ofthe basin is essentially filled as shown in FIG. 4 with a porousstructure consisting of gravel or pebbles 40. Moreover, porous orperforated partitions 41 are advantageously provided within each channelsuch as 33, 34, 35, 36 at intervals along the separating portions of thebasin (FIG. 4).

The basin may be made according to any known suitable process and forinstance according to a process similar to the one which is used forproviding hydraulic dams or weirs for the so-called "earth" dam typesuch as in Serre-Poncon.

In this instance it is only necessary to dig trenches into the groundwhich will form the portions 33, 34, 35, 36 the waste or excavatedmaterial forming the raised or elevated walls of the channels 28, 29,etc.. The walls will be compacted, covered with fine inert material suchas sand and sealed or made impervious in fluid-tight or leak-proofrelationship with sheets or foils of plastic material welded or bondedto one another. The channels may be several hundreds of meters long anda few tens of meters wide and deep.

Upon performing the computations it appears that a few hundreds ofhectares of tank surface area thus formed will be enough to allow theseasonal storage in France of any amounts of hot water released inexcess by the thermal and nuclear power stations during the warm seasonsand the re-use of such a stored heat during the cold seasons.

The working of the plant shown in FIG. 2 is carried out as follows.

The thermal power station 10 discharges its excess hot water through thepipe-line 11 towards the pipe-line 12 and the utilization system 13.When the amounts of hot water supplied by the power station are higherthan the requirement of the users or consumers, the excess hot water isfed by the pipe-line 23 into the tank 22 at the inlet 33b of the channel33. The hot water is flowing slowly and regularly forward within thechannel 33 while driving back gradually ahead of it the interface orseparation front with the cold water which has been assumed to belocated at 42. The hot water taken into the tank will heat up thepebbles and accordingly cool down while flowing forward, therebyconsiderably decreasing the actual speed of travel of the interface orseparation front 42 between the cold water and the hot water withrespect to the speed of flow of the water within the tank. At the sametime the hot water is fed into the tank through the pipe-line 23, thecold water is drawn from the tank through the pipe-line 24.

With a view to restrict the head or pressure losses there may possiblybe provided shorter return circuits or paths for the cold water such asdiagrammatically shown at 43, 44 provided with valves 45, 46, 47. Thusin the embodiment shown in FIG. 2 when the interface or separation frontbetween the hot water and the cold water is located at 42, the valves45, 46 may be closed and the valve 47 may be opened for allowing thereturn of cold water to take place directly between the end 34b of thechannel 34 and the return pipe-line 20 by-passing the channels 35, 36.

When the requirements of the demand are higher than the flow ratesupplied by the power station 10, hot water will be taken from or drawnoff the tank 22 through the pipe-line 23, a corresponding cold waterflow rate being injected at the other end of the tank or also forinstance through the pipe-line 44 in the example shown. In a mannerreverse to the heating up process of the tank described hereinabove thecold water front 42 will advance much more slowly than the cold waterflow rate injected into the tank while taking into account the gradualcooling down of the pebbles.

Thus with a relatively small bulk of stored water which may be or notrecycled wholly or in part, there is provided a seasonal storage of hugeamounts of energy within the bodies or masses of the pebbles of thebasin.

According to another advantageous characterizing feature of theinvention and as will become apparent more clearly in the followingdescription of another embodiment shown in FIGS. 5 to 9, the porousstructure is covered or lined over the surface thereof with animpervious or sealing layer such as a concrete or asphalt layer possiblycovered with a heat-insulating material. This surface which remainstempered in any season is suitable to receive playgrounds or likeplaying areas, concert halls, glasshouse cultivations, etc.

Although in FIGS. 2 to 4 there has been depicted a rectangular basinstructure divided into several longitudinal juxtaposed channels it isobvious that other shapes of basins in particular adapted to localconditions may be selected such as for instance circular, elliptic,spiral and other shapes. In any case one should advantageously contriveto divide the basin into several elongated separation zones which maycommunicate with each other in parallel and/or in series connectedrelationship to enable a good programmed working of the whole surface ofthe basin.

Reference is now made to FIGS. 5 to 9 wherein a particularlyadvantageous process of the making a tank according to the invention hasbeen illustrated.

In FIG. 5 is diagrammatically shown a sectional view of a ratherconventional formation which may be encountered at differentgeographical places and in which there may be found along a river 50 abed of gravel 52 resting on an impervious layer of marl or clay 51 andwhich often is several meters thick, a few hundreds of meters wide andseveral kilometers long. At 53 may be seen one edge, brink or verge ofthe valley consisting of any kinds of grounds.

In such a formation there are provided according to the invention asseen in FIG. 6, fluid-tight walls 54, 55, 56, 57 made for instance fromconcrete and which extend through the thickness of the porous structuresof the pebbles 52, said walls defining between one another channels orseparation zones 58, 59, 60. The concrete partition walls 54, 55, 56, 57may be built according to any suitable process for instance throughcontinuous casting with a travelling shuttering or formwork movingbehind a ripper blade or the like which opens the bed of pebbles down tothe marl layer 51. In such a manner as diagrammatically shown in topview in FIG. 7, there is provided a tank of a general type similar tothat illustrated in FIGS. 2 to 4, comprising channels 58, 59, 60 limitedby channels 54 to 57 and closed at their ends by walls 61, 62.

Towards each end of the channels there are advantageously providedporous partitions 58a, 59a, 60a; 58b, 59b, 60b which will retain thepebbles and leave at each end of the channels spaces 64, 65, 66, 67 inwhich are arranged ducts for interconnecting the channels and/or drawingoff and adding hot water and cold water.

In the tank shown in FIG. 7 the pipe-lines 68, 69 respectively performthe function for instance of the pipelines 23, 26, the inputs andoutputs of hot water taking place at 68 and the inputs and outputs ofcold water taking place at 69.

The junctions 70, 71 correspond to the junctions 37, 38, 39 in FIG. 2.

It is obvious that more than three channels may and will usually beenused and various junctions (not shown) will enable the working oroperation in parallel and/or in series connected relationship accordingto the requirements and to the local layouts of the various separationzones of the tank.

If desired and as illustrated in FIG. 8 the bottom of the tank may beprovided with an insulating layer 72 consisting for instance of injectedplastic foam which will limit the heat losses towards the adjacentgrounds.

The surface of the basin should advantageously be covered with afluid-tight layer for instance of concrete or asphalt 73 which willlimit the evaporation and heat losses and onto which may be arrangedglasshouses 74 for the forcing of plants such as fresh or earlyvegetables, exotic trees (oranges, etc.). Cultivation in the open air orout of doors may also be contemplated.

On ground level there should advantageously be arranged as shown on alarger scale in FIG. 9 over the pebbles 60 a concrete or asphalt layer73 and then a layer of a suitable heat-insulating material 75(glass-wool, plastic foam, etc.). If cultivations are contemplated, alayer of tillable soil or tilth 76 should be arranged above the layers73, 75 and should advantageously be formed with ventilation ducts 77 inparticular for the hot summer-time periods.

Many modifications may of course be brought about to the forms ofembodiment and working examples described which have been given by wayof illustration only.

Thus in particular in the case where the surfaces of the groundsoccupied by the hot water storage is covered with cultivations, inparticular in glasshouses, the basin will advantageously be divided intoseveral zones in which the hot water and cold water will be cycliclydrawn therefrom and fed thereto according to the requirements or needsof the demand while however taking into account the cyclic cultivationscarried out at the surface within said zones.

Moreover in a manner reverse to what has been described it is possibleto store in the tank during winter time cold water, i.e. that which isinjected at the same time the hot water is drawn off and to use the coldwater during summer time as a coolant for condensers, refrigeratingmachinery, heat engines, air-conditioning of rooms and premises, etc..Storages at temperatures lower than 0° C. may possibly be carried out byusing instead of water other suitable solutions such as brines, etc.

According to the embodiment diagrammatically shown in FIG. 10 there isseen a cross-sectional view of a basin 100 which is dug out or excavatedlike a trench within grounds 101, the waste or excavated materialsserving the purpose of forming retaining side dikes or embankments 102,103. Such a basin may of course be given any desired length so as tomatch the amounts of water which are desired to be stored and severalbasins of this kind may be connected in parallel and/or in seriesrelationship while being laid out according to favorable localconditions.

In this basin has been enclosed the bulk of hot water storage 104 insideof a pocket the membrane 105 of which is displaceable and deformable andfor instance made from a sheet of plastic material such as polyvinyl,polyethylene, etc.

Likewise the bulk of cold water storage 106 has been enclosed within apocket the membrane 107 of which may be made in a way similar to that ofmembrane 105. It is advantageous as shown that the bulk of hot waterstorage 104 be positioned above the bulk of cold water storage 106 sothat the lighter hot water will naturally top or overlie the heaviercold water.

According to a particularly advantageous characterizing feature of theinvention both bulks or bodies of storage water 104, 106 are topped by abody of water 108 which will usually be open to the atmosphere and whichthus forms a water surface or artificial lake. In order to limit theheat exchanges between the hot pocket 104 and the body of water 108there should advantageously be provided above the bodies of storagewater an insulating roof 109 made for instance of a plastic foam.

According to an original and interesting characterizing feature of theinvention, in order to provide for a normal stratification orarrangement into overlying layers of the stored waters, waters withspecific gravities or densities and/or saltnesses higher than those ofthe water 108 should be used as storage waters 104, 106. For instancesoft water may be used to provide the water surface 108 and salt waterfor instance sea water or a water loaded with potassium salts, baryumoxide, etc. may be used as the storage water 104, 106. For instance itwill thus be found above at 108 soft water at about 10° C. to 30° C.with a specific gravity of from 1 to 0.996 and for the body 104 hot saltwater for instance sea water having at 90° C. a specific gravity ofabout 1.010 and underneath the same salt water having at about 30° C. to50° C. a specific gravity of 1.013.

As shown in FIG. 11 such a basin is operated as follows.

When an outside heat requirement occurs, for instance to heat buildings,hot water from the storage body 104 is pumped through a pipe-line 110and a pump 111 through a heat exchanger 112, the back flow or return ofcold storage water being effected through the return duct 113 into thebody of cold storage water 106. At 114, 115 has been diagrammaticallyshown the input or return 114 of the cold water of the system and at 115is shown the output of the hot water towards the distribution andutilization system (central heating of buildings in particular).

It is thus found that as the bulk of the body of stored hot water 104decreases, the bulk of the body of stored cold water 106 will increaseaccordingly, the storage tank operating at a substantially constantcapacity or volume except for losses and variations in expansion.

An exchanger of the same kind as the exchanger 112 may of course be usedby reversing the direction of flow through the pump 111 so that when theheat production of the power stations is higher than the requirements orneeds the heat of the waste hot waters discharged by the power stationsmay be used for heating the cold storage waters 106 and convey or feedthem in the re-heated condition into the storage body 104.

According to the alternative embodiment shown in FIG. 12 the body ofcold storage water 106 is enclosed between two yielding or flexible,deformable and movable membranes or diaphragms 120, 121 which areconnected as by bonding or welding and anchored with their edges 122,123 to a flexible insulating roof 124. The body of hot storage water 104is enclosed between the membrane 121 and the roof 124. Above the roof124 there is again the body of water 108 forming the water surface.Except for a difference in construction, the arrangement shown in FIG.12 may operate like that shown in FIGS. 10 and 11.

According to the alternative embodiment shown in FIG. 13, the body 104of hot water storage is this time enclosed between an insulating roof125 comprising for instance an impervious layer of plastic foam and aflexible deformable membrane 126 forming bellows on the sides andproperly anchored as shown at 127, 128, 129, 130 to the brinks or edgesof the basin 100. The anchoring may be made at discrete spots or alongedge lines.

The cold storage water 106 is stored below the roof 125 and outside ofthe body 104. Thereabove is provided the water surface 108. According tothe operating requirements the pocket 104 will become deformed. Therehas thus been shown at 126' another position of the membrane 126 inwhich the tank contains less hot storage water and more cold storagewater.

In FIG. 14 there has been shown another alternative embodiment whereinthe body of hot storage water 104 is enclosed within a pocket defined bya membrane 130 which is protected at the upper part by an insulatingroof 131 which is resting thereon. The body 106 of cold storage watersurrounds the pocket 104 which will automatically float at the topportion owing to the specific gravity of the hot storage water which islighter than the cold storage water. Above the roof 131 is providedagain the water surface 108. In order to provide for a good separationbetween the bodies 106, 108 and allow the motions of expansion of theroof 131 the fluid-tightness of the roof 131 and of its connection withthe edges or brinks of the basin is achieved by means of a flexiblemembrane or diaphragm 132 properly anchored at 133 above the level ofthe water surface 108, which membrane-like sheet 132 is connected to theroof 131. A springing or overhanging portion 134 made for instance fromconcrete protects the relatively fragile flexible sheet 132 againstexternal actions which are likely to tear or rip it open.

At 135, 136 are seen the storage working ducts which perform functionssimilar to those of the ducts 110, 113 in FIG. 11.

According to the alternative embodiment shown in FIG. 15 the body of hotstorage water 104 is divided into several adjacent bodies 104', 104",104"', 104"" which are each one enclosed within a hose-like membrane140, 141, 142, 143 which may extend the whole length of the basin. Thepockets 104', 104", etc. are surrounded by the lower body portion 106 ofthe basin reserved for cold water storage purposes and are floating atthe surface of said body. In the example shown the space 106 is madefluid-tight by means of a flexible membrane 144. Above the storagewaters is advantageously provided a protecting insulating roof 145 whichforms the bottom of the artificial lake filled with the upper body ofwater 108.

In the case where the lake is adapted to serve for instance for aquaticsports it will be advantageous to provide a protecting roof 145 strongenough to remove any danger of damaging the lower portion of the basinholding the storage waters. For this purpose and as shown in FIG. 16 theroof 145 may be made from a sealing sheet 146 which may be fitted tocover the sheet 144 of the body 106 and on which sheet 146 will bearranged blocks of protecting material for instance cellular concreteblocks 147. In order to bear the weight of the roof the lower storagespace of the basin may be subjected as shown in FIG. 15 to a slightwater overpressure by connecting for instance the space 106 through aduct 148 to a small supply container 149 in which will be kept a givenwater level 160 located at the desired height h above the water surface150 of the lake. This slight overpressure will enable to very readilysustain the weight of the roof whatever its nature might be.

According to the alternative embodiment shown in FIG. 17 there are againthree overlying bodies of water namely of cold storage water 106, of hotstorage water 104 and of the water of the lake 108 together with aprotecting roof 151 which may for instance be of a construction similarto that of the roof 145. In this instance as in FIG. 15 a slightoverpressure h should be provided in order to bear the weight of theprotecting roof 151.

The body 104 of hot water and the body 106 of cold water may beseparated from each other by a flexible deformable and/or movablemembrane 152 which may be connected from place to place by means ofrigging lines or ropes 153 to the roof 151. The operation of the tanksmay of course be performed in the same manner in the forms of embodimentwhich have just been described and in the one which has been discussedwhen depicting FIGS. 10 and 11 for instance.

According to the embodiment shown in FIG. 18 there is shown again astructure which has already been described with reference to FIG. 12.There is thus seen a membrane 124 which forms the roof covering the body104 of hot storage water enclosed between the membrane 121 and the roof124. Underneath the body of hot storage water 104 there is provided thecold storage water 106 enclosed between the membrane 121 and a membrane120, the storage comprising more or less bulky relative bodies of hotwater 104 and of cold water 106 according to the season. Above the roof124 is formed a water surface 108 enclosed in a sink or trough of ground101.

The improvements relating to the construction of the "roof" which willnow be described are very well applicable to this kind of tank but alsoto other embodiments of the tank described with reference to the otherFigures.

Reference will now be had to FIG. 19 illustrating the manner of makingthe roof in accordance with these improvments.

According to the embodiment shown herein the membrane of the roof 124 isof a sandwich construction of three layers, namely a top layer 201 whichlets the major part of the light flux pass therethrough, a transparentlayer 202 with a low coefficient of heat conductivity and a layer 203which absorbs the major part of the light radiation received.

For instance the layer 201 may consist of a transparent sheet of plasticmaterial such as transparent butyl rubber or any suitable syntheticmaterial such as for instance a polyester film, a polyethyleneterephthalate resin such as known under the registered trademark "MYLARR" or the like. The layer 202 may consist of a transparent syntheticfoam having a low thermal conductivity. The layer 203 may consist forinstance of a butyl rubber with a carbon black filler.

The light flux, such as for instance solar radiation diagrammaticallydesignated by the arrow 204, after having passed through the top waterlayer 108 travels through the transparent film 201 and then through thetransparent layer 202 and is eventually absorbed by the absorbing layer203. The infra-red radiation re-emitted by the layer 203 is reflected bythe layers 202 and 201 back towards the hot storage water 104 so thatthe heat supply from solar radiation generally enables to compensate toa large extent for the heat losses of the hot storage water towards theoutside. The efficiency is of course not perfect since some part of thesun radiation 204 is reflected back by the water layer 108 and also bythe layers 201 and 202. Moreover all the heat absorbed at the layer 203is not used for heating the hot storage water 104. However with such aconstruction of the tank roof and without any additional expense theoverall efficiency of the plant is improved. By way of example the sheet201 may have a thickness of about one millimeter whereas the layer 202may have a thickness of about 25 mm and the sheet 203 may have athickness of about 2 mm.

According to the alternative embodiment shown in FIG. 20 forconstituting the roof 124 use is made of a composite membrane comprisedof a sandwich construction composed of the films 201 and 203 for exampleidentical with those shown in FIG. 19 which enclose therebetween a gasor fluid 205 which plays the part of the layer 202. Spacers or likebracing members such as rods or threads 206 properly secured to thesheets 201, 203 provide for the proper spacing left between these twosheets.

The nature of the gas or fluid 205 used is selected so as to beconsistent with a good preservation of the sheets 201 and 203 and alsoso as to promote the transmission of heat power in the form of lightfrom the outside towards the tank and to reduce the flow in the reversedirection or outwards from the tank towards the outside of the heatthrough radiation and conduction.

Alternatively there may be used as a fluid 205 for instance water whichmay form a buffer layer at an intermediate temperature between that ofthe hot water layer 104 and that of the upper cold water layer 108reducing the outward directed heat emissions from the tank towards theoutside. This hot water layer 205 may possibly be introduced into thestorage space or mixed with the storage water while adjusting the supplyand mixing flow rates according to the temperature reached by the layer205 in accordance with the actual outside conditions prevailing at thattime. The pressure of the fluid or gas 205 will of course be kept at thedesired value to provide the proper spacing between the sheets 201 and203. The gas may for instance be air or nitrogen introduced under asuitable pressure for instance lower than atmospheric pressure so as toimprove the insulation of the composite membrane. In such a case inparticular the lower layer 203 and/or the upper layer 201 may be made soas to be formed with a bright bottom surface 203a, 201a in order to takeadvantage of the DEWAR effect.

According to the alternative embodiment shown in FIG. 21 the sheets 201and 203 enclose therebetween a layer 207 comprised of a cellular plasticfoam with oriented cells having their major size surfaces extendingsubstantially horizontally. This foam should be selected so aspreferably to be transparent or in particular translucent so that theouter light radiation may travel easily therethrough whereas theorientation of the cells will reduce the outward directed heat emissionthrough radiation and conduction from the storage space towards theoutside.

According to the embodiment shown in FIG. 22 the roof 124 separating thecold water 108 from the hot water 104 essentially comprises a layer 208absorbing the outer light radiation, made of for instance a layer ofheavy hydrocarbon. This hydrocarbon layer may be arranged upon afluid-tight film 209 for instance in a manner similar to that which hasbeen described previously in particular with reference to thedescription of FIGS. 15 and 16.

By selecting the layer 208 to be thick enough it will both perform afunction of mechanical protection of the tank roof and a function ofstoring solar heat capable of compensating for at least a major part theoutward directed heat losses from the storage space towards the outside.Moreover the layer 208 will promote a certain temperature increase ofthe cold water 108 which may be favorable for fish-breeding or forbuilding swimming pools.

The application procedures which have been described of the improvementsto the construction of the roof may of course be applied to most of thedescribed embodiments of the invention. The essential idea resides inproviding the roof of the storage space so as to promote the conveyanceof outer heat due to the solar radiation towards the hot water storageand to reduce the conveyance of heat from the storage space towards theoutside.

What is claimed is:
 1. A large-capacity tank for seasonal storage of hotwater, produced for example by electric power generating thermal andnuclear stations, and for their seasonal use, for example for theheating of buildings, comprising:a basin of large surface area;partition walls provided in said basin dividing said basin into aplurality of distinct elongated storage zones, each elongated storagezone having two separated ends; first means coupled to one end of eachof said elongated storage zones for supplying and recovering hot waterstored in said elongated storage zones; second means coupled to theother end of each of said elongated storage zones for supplying andrecovering cold water stored in said elongated storage zones; and meanscoupled to said first and second means for controlling the flows ofwater such that an instantaneous supply of hot water at one end of oneof said elongated storage zones is balanced by a corresponding drawingoff of cold water at the other end of another of said elongated storagezones, and such that an instantaneous drawing off of hot water at oneend of said one elongated storage zone is balanced by a correspondingsupply of cold water at the other end of said another elongated storagezone, said one and another elongated storage zones providing together asubstantially constant body of storage water.
 2. A tank according toclaim 1, wherein said basin is divided into several zones formingchannels in which said hot water is stored.
 3. A tank according to claim1, wherein said elongated storage zones have a great length with respectto their width and to their depth and communicate with one another inparallel and/or in series connecting relationship through their adjacentlongitudinal ends.
 4. A tank according to claim 3, comprising porous orperforated partitions located at intervals along said elongated storagezones.
 5. A tank according to claim 1, wherein the volume of said basinis essentially filled with a porous structure.
 6. A tank according toclaim 5, wherein the thickness of said porous structure ranges fromabout a few meters to a few tens of meters.
 7. A tank according to claim5, wherein said porous structure is provided at its surface with asealing layer made from concrete.
 8. A tank according to claim 5,wherein said porous structure is provided at its surface with a sealinglayer made from asphalt.
 9. A tank according to claim 7 or 8, whereinsaid sealing layer further comprises a heat-insulating layer.
 10. A tankaccording to claim 5, wherein said basin is filled with pebble-typematerial.
 11. A tank according to claim 10 wherein said pebble-typematerial is provided between said partition walls, said partition wallsbeing porous.
 12. The tank according to claim 10, wherein said basin isa generally rectangular structure, and said partitions extendlongitudinally thereof to provide juxtaposed channels containing saidpebble-type material.
 13. The tank according to any one of claims 10, 11or 12, wherein said pebble-type material comprises gravel.
 14. A tankaccording to claim 1 in particular for storing hot water, wherein theupper portion of said tank is provided with a roof under which said hotwater is stored, which roof promotes the conveyance of outer heat due tosolar radiation towards the stored hot water and reduces thetransmission of heat from said storage space towards the outside.
 15. Atank according to claim 14, wherein said roof forming a membranecovering the body of stored hot water comprises at least one layerformed with a bright face directed towards the storage space.
 16. A tankaccording to claim 14, wherein said roof comprises at least one layerabsorbing light radiation and in contact with the stored hot water andat least one upper layer allowing the major part of the light flux topass therethrough and reflecting a major part of the infra-red radiationre-emitted by said absorbing layer.
 17. A tank according to claim 16,wherein said upper layer comprises a film of transparent plasticsmaterial selected from the group comprising transparent butyl rubber andpolyethylene terephthalate.
 18. A tank according to claim 16, whereinsaid absorbing layer comprises a film made from plastic materialselected from the group comprising butyl rubber and polyethyleneterephthalate filled with carbon black.
 19. A tank according to claim16, wherein said absorbing layer and said upper layer are separated by atransparent layer having a low coefficient of thermal conductivity. 20.A tank according to claim 19, wherein said transparent layer with a lowcoefficient of heat conductivity comprises of a synthetic foam withproperly oriented cells.
 21. A tank according to claim 19, wherein saidtransparent layer with a low coefficient of thermal conductivitycomprises of a layer of suitable fluid kept under proper pressure so asto provide for the desired spacing between said absorbing layer and saidupper layer.
 22. A tank according to claim 21, wherein said fluid layerbetween said absorbing and upper layers is a gas selected from the groupcomprising air and nitrogen and kept under a pressure lower thanatmospheric pressure.
 23. A tank according to claim 21, wherein saidfluid layer comprises a gas layer.
 24. A tank according to claim 1,wherein said zones to which are leading the systems supplying hot waterfrom said power stations and those to which are leading at least one ofthe supplies of cold make-up and return water of said utilizationsystems are in mutual contact while being separated from one another byat least one flexible movable membrane which separates said storagezones into at least one hot water storage space and at least one coldwater storage space which provide together a substantially constant bodyof storage water.
 25. A tank according to claim 24, wherein said hotwater storage zones are immersed within the upper portions of said coldwater storage zones.
 26. A tank according to claim 24, wherein the upperstorage zones are provided with an insulating roof above which is formeda body of water the bottom of which is constituted by said roof.
 27. Atank according to claim 26, wherein said roof comprises a flexibledisplaceable sheet.
 28. A tank according to claim 27, wherein said roofcomprises a strong protecting lining provided above said flexible sheet.29. A tank according to claim 27 or 28, wherein said flexible sheet isdeformable.
 30. A tank according to claim 28, wherein said storage zonesare subjected to a gauge overpressure with respect to the level of saidbody of water, said overpressure bearing the weight of said roof.
 31. Amethod of operating of storage tank built according to claim 26,comprising the steps of using, for filling the volume of said body of, awater having a specific gravity lower than those of said stored hotwaters and cold waters.
 32. The method according to claim 31, whereinsaid water filling the volume of said body of water has a saltinesslower than those of said stored hot waters and cold waters.